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Computer-to-printer communications
A computer and printer communicate by means of numbered
codes. If you press the letter A on the keyboard, it is translated
into a numeric code, transmitted to a peripheral device (such as a
video screeen or a printer) then displayed as the letter A.
To cope with the many different kinds of computers and print-
ers used today, a standard set of codes has been developed. This
set of codes is called the American Standard Code for Information
Interchange, or ASCII for short. Almost all computers use these
ASCII codes to communicate with printers.
There are ASCII codes for all of the letters in the alphabet, both
upper- and lowercase, and for the numbers from 0 to 9. The
ASCII code also includes most punctuation marks, and some
codes that control printer functions. If you refer to the ASCII chart
in Appendix B, you'll find that all of these letters, numbers and
punctuation marks have been assigned code numbers from 33
through 255.
ASCII codes
Although these codes are standard from computer to compu-
ter, they can be expressed in a number of different ways. The
chart in Appendix B is a comparative table that lists each ASCII
code as a character (A, B, C, 1,2,3) and as a decimal or hexadecimal
number. For example, the letter A is represented as an A and as
the decimal number 65. If you wanted to print the letter A using
the BASIC language, you would use the decimal notation, writ-
ten as CHR$(65).
The chart also shows the hexadecimal (or hex) value of each
character. The hexadecimal numbering system is based on units
of 16; our usual numbering system, decimal, is based on units of
10. In hex, the letter A is expressed as 41H (the H stands for
hexadecimal).
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